In order to meet government and military specifications, turbine oil compositions must score well on a number of standard tests including those that measure the capacity of the turbine oil's load-carrying ability. Additives, such as amine phosphates, alkylthiosuccinic acids, thiphene carboxylic acid derivatives, and other sulfur-containing compounds have been used to improve the load-carrying capacity of ester base turbine oils.
Ester base lubricating oil compositions prepared from pentaerythritol and a mixture of fatty acids and containing selected additives, such as those recited above for improvement in load-carrying capacity, are well known and have been somewhat successful in increasing the turbine oil's load-carrying ability. However, deleterious effects on other desirable features often accompany the improvement in load-carrying ability of these modified turbine oils. In particular, the score of these oils in industry standard tests that measure deposit formation under simulated wear tends to deteriorate. There is a continuing need for additives that improve the load-carrying capacity of turbine oils without deleteriously affecting other salient properties of the turbine oil such as oxidative stability, viscosity and TAN increase. This invention addresses that continuing need.